Conventionally, there are a variety of types of wind power generators, and each type of wind power generator has different characteristics. For example, when classifying wind power generators by the direction of attachment of a shaft for supporting a windmill, they are divided into a vertical shaft type the direction of attachment of the shaft of which is vertical and a horizontal shaft type the direction of attachment of the shaft of which is horizontal. The vertical type includes the Savonius windmill, the Darius windmill and the like, and the horizontal type includes the propeller type and the like.
When classifying them with regard to whether they function predominantly based on a torque for rotating a windmill, generated by drag or lift, they are divided into a drag type in which drag mainly functions, a lift type in which lift mainly functions and a drag/lift type in which each of drag and lift functions to a similar degree. For example, the Savonius windmill is of the drag type, and the Darius windmill and the propeller type are of the lift type.
Since for example, a drag type windmill is rotated well by weak winds or so-called breezes, it can generate power from weak winds. However, when generating large amounts of power, equipment becomes structurally large and accordingly uneconomical.
If the blade area of a drag type windmill is made large in order that it might be rotated even by a weak wind, at the time of strong winds, wind force from the rotating direction works against the rotation and the resistance becomes large proportional to the size of blades. Accordingly, the power generating efficiency degrades, which is a problem. However, a lift type windmill can be used not only for low power generation but also can easily be used for high power generation. Simultaneously, for example, some small lift type windmills can generate power of 400W from winds of a velocity of 12.5 m/second.
However, a lift type windmill requires wind of a high velocity as a rotation starting velocity which is the wind velocity needed to rotate a windmill to generate power. Therefore, it cannot be rotated by weak winds and sufficient power generating efficiency cannot be obtained, which is a problem.
If the blade elevation against a wind direction of a lift type windmill is increased in order for the windmill to be rotated even at the time of strong winds, drag increases and becomes a resistant force against the rotation of the windmill. Accordingly, the rotation efficiency of the windmill degrades.
However, as a method for solving this problem of a lift type windmill, a method for providing a windmill with a wing angle adjustment function and rotating the windmill even at the time of weak winds by this adjustment function unlike a conventional fixed wing angle type windmill is proposed (for example, see Patent reference 1).
Patent Reference 1:
Japanese Patent Application Publication No. H8-322297 “Wind Power Generator” (Abstract, representative drawings)
Recently, demand for a small-sized wind power generator has been high demand and arises from the viewpoint of earth environment preservation. However, providing such a small-sized wind power generator with the above-mentioned wing-angle adjustment function leads to high cost of the device, which is not preferable since it goes against the trend of a low cost underlying the essential desire for a small size.